The present invention generally relates to image processing systems, and more particularly, to image processing systems used to control vehicle equipment, such as vehicle headlamps, windshield wipers, etc.
Recently, many vehicular control accessories utilizing image processing systems have been proposed. For example, U.S. Pat. No. 5,837,994 entitled xe2x80x9cControl System to Automatically Dim Vehicle Head Lamps,xe2x80x9d commonly assigned with the present invention and hereby incorporated by reference, discloses a control system which utilizes an image sensor and a processor to detect the headlamps of other vehicles at night and automatically control the state of the high beam headlamps of a vehicle. Another example of an image processing system to control vehicle equipment is given in U.S. Pat. No. 5,923,027 entitled xe2x80x9cMoisture Sensor and Windshield Fog Detector,xe2x80x9d also commonly assigned with the present invention and hereby incorporated by reference. This patent discloses an image processing system, which acquires images of a vehicle windshield in order to detect the presence of rain or fog.
In each of these systems, as well as several other disclosed automotive image processing systems (see, for example, U.S. Pat. Nos. 5,765,116, 5,675,489, and 5,660,454 and PCT Published Patent Application No. WO 00/53465), images are acquired by an image sensor and stored into a memory in their entirety for subsequent processing. While technically very convenient, the use of this amount of image memory presents problems when adapting the system for commercial use, especially in the highly cost-sensitive automotive market. Most low cost microcontrollers or digital signal processors (DSPs) suitable for these types of applications are equipped with only a few hundred bytes to a few kilobytes of random access memory (RAM) into which the images can be stored. The processing core of many microcontrollers is typically available with a variety of RAM configurations, with the price increasing as the amount of memory increases. Therefore, it is advantageous to use a microcontroller with the least amount of RAM possible. The use of a small amount of RAM in prior art systems limits the size of the image, which can be stored and thus greatly limits the resolution.
A common off-the-shelf image sensor may have 352xc3x97288 pixels, known as the CIF format. Storing an entire image from this sensor requires approximately 100 kilobytes of RAMxe2x80x94far more than is typically available on a low cost microcontroller. Some microcontrollers have the ability to increase the amount of RAM available by the addition of an external memory chip. These microcontrollers must have an external memory bus, increasing the pin count and thus the cost and complexity of the microcontroller and the circuit board to which it is attached. The cost of the external memory itself must also be considered, and despite rapid memory price declines, this cost is anticipated to remain significant for some time to come. Finally, if an image must be transferred to memory before it can be processed, the total time required to acquire and analyze an image will be greater than if the analysis could occur simultaneously with the acquisition.
What is needed is a low cost image processing system to control automotive equipment which is capable of analyzing images without first storing them to memory, thus reducing the total amount of memory required in the system.
The present invention solves the problem of the prior art by providing an image processing system, which does not require a memory with enough storage locations to store the digital grayscale value of every pixel in the image. The system contains an image sensor array containing a plurality of pixels, each of which is configured to provide an output indicative of the amount of light received by the pixel over the exposure time. The system also provides an analog-to-digital (A/D) converter to quantize the signal from the pixel into a digital grayscale value. The system also provides a processor in communication with the image sensor and A/D converter to analyze the images acquired by the image processor and control vehicle equipment based upon the results of processing the images. Finally, the system contains a memory for storing the grayscale value of some of the pixels and for storing other data used by the processor. By providing an image processing system with less available memory than is needed to store all pixels, the cost and the complexity of the image processing system can be reduced.
According to one aspect of the present invention, the amount of memory required is reduced by acquiring and analyzing only a portion of the image at a given time. This may be accomplished by acquiring a single row of pixels at a time or by acquiring a subwindow of pixels, which is a subset of the window containing all the pixels.
In another aspect of the present invention, a digital image processing filter is implemented by only storing a most recent group of pixels and performing the filter algorithm on this group of pixels. The most recent group of pixels may be, for example, the last few rows of the image received. The system performs the filter algorithm on the last few acquired rows and discards the oldest row as a new row is acquired.
In another aspect of the invention, some of the pixel values received by the processor are discarded as they are received and only a subset of the values is stored in the memory. Pixels may be discarded at a uniform rate throughout the image or at a non-uniform rate. For example, pixels may be discarded at a high rate near the periphery of the image and at a low or zero rate near the center of the image to provide a greater resolution near the center of the image.
In another aspect of the invention, the values of adjacent pixels may be averaged with one another and a single value stored in memory representing the average of several adjacent pixels. The number of pixels averaged with each other may be uniform throughout the image or may be non-uniform. Many pixels may be averaged with each other near the periphery of the image and few or zero pixels may be averaged with each other near the center of the image to provide a greater resolution near the center of the image.
In another aspect of the invention, objects identified in the image may be extracted from the image and stored as the image is being acquired. For example, the present invention may be used to identify headlamps of oncoming vehicles in order to determine the high beam state of the headlamps of the controlled vehicle. The present invention can identify the presence of an oncoming headlamp in the image as it is being acquired and store various information about the headlamp in an object list.
In another aspect of the present invention, the image data may be compressed as it is being acquired. This compression is accomplished by many ways including reducing the number of quantization levels (bit depth) of a pixel value as it is being received. Reducing bit depth of the image may be performed either uniformly or non-uniformly across the image and by requantizing either linearly or non-linearly. This aspect of the present invention is particularly useful for reducing data rate when the camera is positioned away from the processor.
In another aspect of the present invention, image data is reduced by storing segments of connected pixels, which together make up an object of interest. For example, a string of connected pixels in one row of an image, all with grayscale values above a threshold, may be stored as one object. Rather than storing the grayscale values of each pixel, only the starting and ending pixels and the cumulative grayscale value of all the pixels are stored. In a color implementation, the average color of the segment may be stored. Finally, two dimensional groups of objects may also be stored. This aspect is particularly useful for greatly reducing the memory requirements and transmitting image data with the least possible overhead. The processing to reduce the image to a list of segments may be contained in the image sensor itself, in a companion processor (ASIC, microcontroller, DSP or the like) near the image sensor, or in the main processor.
In another aspect of the present invention a color image sensor is used to detect color information about an object in the scene. In this embodiment, multi-layer thin film interference filters are placed over each pixel in a checkerboard or mosaic pattern such that adjacent pixels are exposed to different spectral bands of light. The use of multi-layer thin film interference filters allows the implementation of a color imaging system in an automotive environment. Typical polymer color filters would be degraded by direct focusing of the sun onto the array which will occur when the vehicle is traveling or is parked such that the camera is in direct view of the sun.
To achieve these and other aspects and advantages, the imaging system of the present invention comprises an image array sensor including a plurality of pixels, each of the pixels is operable to generate a signal indicative of the amount of light received on the pixel; an analog to digital converter for quantizing the signals from the pixels into a digital value; and a memory including a plurality of allocated storage locations for storing the digital values from the analog to digital converter, wherein the number of storage locations in the allocated memory is less than the number of pixels in the image array sensor.
According to another embodiment of the present invention, a control system is provided to control the headlamps of a vehicle. The control system comprises: an image array sensor including a plurality of pixels, each of the pixels is operable to generate a signal indicative of the amount of light received on the pixel; an optical system configured to image the scene forward of the controlled vehicle onto the image array sensor; an analog to digital converter for quantizing the signals from the pixels into a digital value; and a control circuit for processing the image of the scene obtained from the imaging system and for controlling the brightness of the headlamps in response to objects detected in the processed scene. The control circuit including a memory including a plurality of allocated storage locations for storing the digital values from the analog to digital converter, wherein the number of allocated storage locations in the memory is less than the number of pixels in the image array sensor.
According to yet another embodiment of the present invention, a control system is provided to control the headlamps of a vehicle. The control system comprises: an image array sensor including a plurality of pixels, each of the pixels is operable to generate a signal indicative of the amount of light received on the pixel; an optical system configured to image the scene forward of the controlled vehicle onto the image array sensor; and a control circuit for processing the image of the scene obtained from the imaging system and for controlling the brightness of the headlamps in response to objects detected in the processed scene, wherein the control circuit generates a segment list identifying segments of adjacent ones of the pixels that generate a signal having a grayscale value above a threshold as the signals are received from the pixels.
According to another embodiment of the present invention, an inside rearview mirror assembly for a vehicle comprises: a mirror mount adapted to be mounted inside the vehicle in a location proximate to or on the front windshield of the vehicle; a mirror bezel coupled to the mirror mount; a mirror mounted in the mirror bezel; an imaging system mounted to the mirror mount and configured to image the scene forward of the vehicle; and a control circuit electrically coupled to the imaging system for processing the image of the scene obtained from the image array sensor and for performing predetermined function in response to objects detected in the processed scene, wherein at least a portion of the control circuit is mounted to the mirror mount.
According to still another embodiment of the present invention, an imaging system for a vehicle is provided that comprises: an image array sensor; an optical system configured to image the scene forward of the controlled vehicle onto the image array sensor; and a control circuit coupled to the image array sensor for processing the image of the scene obtained from the image array sensor to control the vehicle headlamps in response to objects detected in the processed scene, the control circuit further processes the scene obtained from the image array sensor to perform at least one of the following functions: (a) to generate a collision avoidance warning; (b) to control the speed of the vehicle; and (c) to generate a lane departure indication signal.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.